The invention relates to a switching device according to the preamble of the independent claim.
Switching devices are equipment used for opening and closing a current circuit. A switching device comprises at least one pole and a control device arranged to open and close this pole. Switching devices include e.g. switches and switch-fuses.
When a current circuit is opened, an electric arc whose temperature is thousands of degrees may occur in a switching device. An electric arc includes ionized gas which contains a large number of free electrons. Such a gas plasma is electrically conductive.
In addition to the electric arc being conductive, metal which has been vaporized from contacts by the electric arc may, upon solidification, impair the insulation capacity of the surfaces of the switching device. Soot produced by the electric arc may also cause insulation problems.
Switching devices wherein air is used as an insulating material comprise a discharge route for heated air. The discharge route enables expanded gas to discharge from the frame of the switching device, which prevents pressure inside the switching device from becoming too high.
A problem with the known switching devices is that in connection with a switching event, gas discharging from the frame of the switching device may cause an earth fault between a live part of the switching device and an adjacent earthed part.